The BBC was last night plunged into a row over claims of "disgraceful" bias in favour of the British National Party.

Anti-fascist campaigners Searchlight launched a formal complaint with BBC director general Mark Thompson after a series of broadcasts which, the organisation said, broke strict election rules on impartiality. Searchlight said the BBC was claiming the BNP were the main beneficiaries of the "anti-politics" sentiment caused by the MPs expenses scandal, when in fact the UK Independence Party and the Greens were ahead of the far-right party in the polls.

A BBC spokesman said the corporation "is obliged to treat all political parties... with due impartiality" and said the BBC "strongly contest" Searchlight's allegations.